This research will be done in Kenya as an extension of NIH grant 1 R01 AI 43415-01A1. The first and third specific aims of this parent grant, entitled "Waterborne Emerging Diarrheal Diseases Study (WEDDS)," have as their underlying goals the identification of any linkages between the ingestion of drinking Water and human cryptosporidiosis. The WEDDS study is being conducted in Massachusetts, where exposure to Cryptosporidium parvum (CP) is moderate compared to developing world environments. Cryptosporidium is an opportunistic pathogen in people with AIDS, and is very common in children. We propose to expand the sites, populations studied, and range of exposures to CP studied by the Parent grant, by replicating specific portions of the study in Greater Meru, Kenya. The site we have chosen is a complex ecosystem with significant human and game park animal interactions. Meru town is adjacent to Meru National Park, the third largest conservation area in Kenya, and Meru town and a number of rural villages share their water supply with the animals of the National Park. Recent studies have shown that humans can be infected with many genotypes of Cryptosporidium, including those from birds (C. meleagridis) and from cats (C. fells) as well as from humans and cattle ("genotypes 1 and 2") and other animals. Human volunteer information has shown that some C. parvum (e.g. the TAMU strain studied in Texas) is both highly virulent and infectious, whereas other strains are orders of magnitude less infectious. The Meru region offers an unusual opportunity to study the connection between human and animal sources of exposure, and to gain some insight into any differences in the severity of disease that may relate to these different genotypes. Our aims are: 1. Conduct a prospective clinical and molecular assessment of Cryptosporidium infecting humans in a region expected to have high exposure to multiple genotypes of Cryptosporidium via its water supply. 2. Isolate, and if possible characterize the genotypes of, Cryptosporidium in waters used by the human population, focusing on (1) Meru town, and (2) rural villages and pastoral areas in the region. 3. Via time-series and geographical information systems (GIS)statistical analysis, delineate the linkage between drinking water exposure and human disease over time.